Reflective active matrix displays are well known and different types of reflective display are known. Reflective displays have a significant advantage of low power consumption, but they can generally only be viewed when there is sufficient ambient light. One solution to this problem is to provide a front or back light for operation in dark conditions. This form of lighting gives rise to deteriorated image quality and increased power consumption. In particular, front lighting can affect the brightness and contrast of the displayed image, especially when the display is being used in its reflective mode.
Matrix display devices employing electroluminescent, light-emitting, display elements are also well known. The display elements may comprise organic thin film electroluminescent elements, for example using organic polymers and molecules, or else light emitting diodes (LEDs) using traditional III-V semiconductor compounds. Recent developments in organic electroluminescent materials, particularly polymer materials, have demonstrated their ability to be used practically for video display devices. These materials typically comprise one or more layers of a semiconducting conjugated polymer sandwiched between a pair of electrodes, one of which is transparent and the other of which is of a material suitable for injecting holes or electrons into the polymer layer.
Visual displays generally operate as either emitting displays (e.g. TV screens/computer CRTs) which operate well in low ambient light environments, or absorption/reflection displays (electrochromic) for applications when ambient light is required to view. Ambient light levels can vary significantly, such as in an environments which pass between dark and light states. Thus, in such environments conventional emitting displays consume significant energy for operation during intervals when the ambient light is sufficient for lower energy consumption allowing absorptive/reflective displays to be used.